In the art of manufacturing pneumatic tires, rubber flow in the tire mold or minor differences in the dimensions of the belts, beads, liners, treads, plies of rubberized cords, etc., sometimes cause non-uniformities in the final tire. Non-uniformities of a sufficient amplitude will cause force variations on a surface, such as a road, against which the tires roll which produce vibrational and acoustical disturbances in the vehicle upon which the tires are mounted. Regardless of the cause of the force variations, when such variations exceed an acceptable maximum level, the ride of a vehicle utilizing such tires will be adversely affected.
Methods have been developed in the past to correct for excessive force variations by removing rubber from the shoulders and/or the central region of the tire tread by means such as grinding. These correction methods are commonly performed with a tire uniformity machine, which includes an assembly for rotating a test tire against the surface of a freely rotating load wheel. In this testing arrangement, the load wheel is moved in a manner dependent on the forces exerted by the rotating tire and those forces are measured by appropriately placed measuring devices, e.g., load cells. When a tire being tested yields less than acceptable results, shoulder and center rib grinders are used to remove a small amount of the tire tread at precisely the location of non-uniformities detected by the measuring devices. As the tire is rotated, it is measured and ground simultaneously. In a sophisticated tire uniformity machine (TUM), such as a Model No. D70LTW available from the Akron Standard Co. of Akron Ohio, the force measurements are interpreted by a computer and rubber is removed from the tire tread using grinders controlled by the computer. Examples of tire uniformity machines utilizing these methods are disclosed in U.S. Pat. Nos. 3,739,533, 3,946,527, 4,914,869, and 5,263,284.
Any vibration that is generated by the tire uniformity machine is detected by its force variation measuring elements, i.e., the load cells. Small quantities of vibration caused by extraneous sources are acceptable because electronic filters are used to remove this extraneous noise. But when the motor bearings wear out, or the grind wheels are defective or improperly installed, or noise and vibration from machines external to the tire uniformity machine are present, excessive vibration will occur. Detection of this excessive vibration by the force measuring elements, i.e., the load cells, can cause inaccurate measurement of the force variations of the tires being measured on the tire uniformity machine. This in turn can result in the tire tread being ground at the wrong locations to eliminate excessive force variations of the tires, resulting in longer grind times, fewer tires processed, and more scrap tires.
Currently, the prior art method of detecting excessive vibration is to use an external vibration analyzer with a movable accelerometer, which a technician manually locates on different points of the tire uniformity machine. Problems with this technique are that the equipment is costly, it takes several hours to complete the vibration analysis, and the resulting downtime of the tire uniformity machine is expensive. Also, since defects in the machine are usually discovered on an infrequent basis, problems are often not discovered before more costly damage results.
As discussed above, efforts have been, and are continuously being made to more improve the accuracy with which tire non-uniformity is corrected. Nothing in the prior art, however, suggests constantly detecting and correcting for extraneous vibration in the tire uniformity machine both prior to and while the force variations in the tire being corrected is measured and reduced through tire grinding.